In steel reinforced concrete structures static strength of the steel reinforcing bars or associated couplers or splices has received most attention. However, as larger and more complex structures are designed using steel reinforced concrete, there has developed a need for a steel reinforcing bar splice system having greatly increased dynamic strength.
It has been discovered by significant testing that the weakest point in fatigue in a taper thread reinforcing bar splice is in the area of the partial threads on the bar which are formed at the ribs or deformations on the outside of the bar. This area of the bar threads is that area covered by the mouth of the coupler. The bar develops fatigue sensitivity at the first engaged partial thread, caused by the inability of the partial threads to transfer significant load into the corresponding portion of the sleeve. Accordingly, in fatigue testing to failure of conventional taper threaded reinforcing bar couplings, most failures are bar failures occurring at the mouth of the coupling sleeve.
It has been discovered that taper threaded reinforcing bar splices can achieve significantly greater dynamic strengths if the elongations of the coupler sleeve and bar are coordinated. This is difficult to do and still maintain a shape to the coupler sleeve which is both serviceable and easy to manufacture.
It is also important that a taper thread splice for reinforcing bar be developed having greatly improved dynamic strength without compromising static performance.